Heidelberg, Germany, July 3rd, 2015

Two main factors influence the cadmium atom's hyperfine structure. First, electrons orbiting the nucleus create a magnetic field resulting in a force affecting the nucleus, and splitting its absorption and emission line into a number of finer lines. Second, there are influences from the way the charge is distributed within the nucleus - a quantity known as the nuclear electric quadrupole moment, which only appears for non-spherical distributions. Some nuclei are shaped like a rugby ball, a frisbee or even a pear.

A peculiar outcome of this study of Cd's hyperfine structure was the observation of a very regular anomaly in the magnetic distribution inside the nucleus - previously observed only in mercury - pointing to a possible general feature of nuclei.

The nuclear properties identified from such precision measurement have both theoretical and practical implications in astrophysics, nuclear and plasma physics. They are also important for detection methods such as atomic, chemical and solid-state spectroscopy, as well as nuclear magnetic resonance.